Mammals reproduce by sexual intercourse. During sexual intercourse, the male inserts his penis into the female's vagina and ejaculates millions of sperm. Conception occurs if one of the sperm fertilizes an ovum (the female egg). After fertilization, the embryo becomes implanted in the female's uterus and begins to develop. Sperm are produced in the testes and travel through a number of ducts before leaving the body. Upon leaving a testis, sperm first travel through the epididymis, a coiled duct lying on the lateral edge of the testis. Sperm then travel through the vas deferens, a tube having a relatively small lumen (internal passageway) and a thick muscular coat which runs upward to a location just above the prostate gland. The vas deferens contains an enlarged section, known as the ampulla, near the point where the seminal vesicle joins. The common duct formed by the union of the vas deferens and seminal vesicle is known as the ejaculatory duct. The two ejaculatory ducts open into the urethra. The urethra runs the length of the penis and opens at its tip. Sperm continually enter the epididymis and, to a lesser degree, the vas deferens. During ejaculation, peristaltic muscular contractions force the sperm to flow through the vas deferens and the urethra.
It is sometimes desirable to prevent conception during sexual intercourse. In the case of certain livestock, man often wants to control which male animal fertilizes a female. In the case of man himself, one or both partners may want to prevent conception and pregnancy. There are many methods of contraception currently practiced. One of the most effective methods is to prevent the flow of sperm through the vas deferens. In a surgical procedure known as a vasectomy, the vas deferens is cut, a section is removed, and the two loose ends are sealed shut. This procedure is relatively safe and is performed relatively easily. Unfortunately, a vasectomy suffers from one very serious disadvantage--it usually cannot be successfully reversed.
There are several factors contributing to the irreversibility of a vasectomy. First, it is difficult to reconnect the two severed ends of the vas deferens. Second, the "downstream" segment of the vas deferens (the segment joining the ejaculatory duct and urethra) tends to necrose over time. This necrosis occurs because the blood supply and nerves supplying the vas deferens are disrupted by the severance. A necrotic section of vas deferens is unable to convey sperm and is very difficult to repair. Third, the "upstream" segment of the vas deferens (the segment communicating with the epididymis) also tends to necrose over time. This necrosis occurs because the testis continues to produce sperm and the sperm continue to flow into the vas deferens. Without an exit, pressure builds within and enlarges and weakens the vas deferens. The vas deferens eventually ruptures, in a manner analogous to an over-inflated balloon. A ruptured vas deferens is nearly impossible to repair.
A number of devices have been disclosed which attempt to control the flow of sperm through the vas deferens, and yet provide a reversibility lacking in a vasectomy. One type of such devices are plugs (also known as intra-vasal occlusion devices) which are inserted into the vas deferens through an incision. These plugs offer the advantage of not requiring a complete severance of the vas deferens. Unfortunately, the plugs suffer from one of two disadvantages: They either permit sperm to pass or they lead to a necrosis and rupturing of the vas deferens.
Braley, U.S. Pat. No. 3,422,813, issued Jan. 21, 1969; Brodie, U.S. Pat. No. 3,648,683, issued Mar. 14, 1972; and Bucalo, U.S. Pat. No. 3,877,461, issued Apr. 15, 1975; disclose intra-vasal plugs. However, the upstream pressure in the vas deferens eventually expands the vas deferens in the vicinity of the plug, allowing sperm to bypass the plug. As a result, these plugs do not completely stop the emission of sperm during ejaculation.
Other plugs are specifically designed to stop the bypassing of sperm caused by expansion of the vas deferens. As one example, Nuwayser, U.S. Pat. No. 3,687,129, issued Aug. 29, 1972, discloses a plug having a fabric coating which allows for the in growth of cells from the wall of the vas deferens. Other examples include Lee, U.S. Pat. No. 3,589,355, issued Jun. 29, 1971; Denniston, Jr., U.S. Pat. No. 4,200,088, issued Apr. 29, 1980; and Zaneveld, U.S. Pat. No. 4,512,342, issued Apr. 23, 1985. These three patents disclose plugs containing various features preventing the vas deferens from expanding around the plug. These plugs may succeed in forming a total barrier. However, pressure increases upstream of the plug and the vas deferens enlarges and eventually ruptures.
Valves and filters are other types of intra-vasal devices which attempt to control the flow of sperm through the vas deferens and yet provide reversibility. Bucalo, U.S. Pat. No. 4,024,855, issued May 24, 1977, discloses a valve which completely shuts off the flow of fluid when closed. Bucalo, U.S. Pat. No. 3,991,743, issued Nov. 16, 1976; and Bucalo, U.S. Pat. No. 4,013,063, issued Mar. 22, 1977; disclose filters which are mounted in the vas deferens and which retain sperm, but let other parts of the fluid pass. None of these valves or filters has achieved any widespread usage. It is believed that all these devices plug relatively quickly and eventually lead to a rupturing of the upstream portion of the vas deferens.
Accordingly, a demand still exists for a method of contraception for males which is as effective as a vasectomy, but is easily and successfully reversed.